The wife of an Norwegian king gave birth to a son during the night. His servants were not sure the baby would live to see the next day so they decided to give him the name of a famous French king, Carlo Magnus. They did not know that Carlo was his name and Magnus meant "the great". So that is how Magnus became a name in Scandinavia.

This name is well known by children in England because of the Roald Dahl tale of "Matilda". In it, Magnus is the father of the protagonist's teacher, Miss Honey. Matilda impersonates him with the help of her telokinesis powers in an effort to scare the wicked headmistress away from the school.